Line of site is a guideline, not an enforceable law.
I'm new here, and I certainly can understand being confused about rules, guidelines and laws, because I am.
The AMA has a safety code that (apparently) members of the AMA must abide by. In the Radio Control section, they state:
"The pilot of an RC model aircraft shall:
(a) Maintain control during the entire flight, maintaining visual contact without enhancement other than by corrective lenses prescribed for the pilot."
So, this issue seems to have layers to it. If you are not a member of the AMA, you are only bound by guidelines that you should maintain VLOS, and that you could be charged with recklessness if you don't maintain VLOS, or maybe even if you do.
On the other hand, if you become a member of the AMA, you sign up for another layer of rules that you must abide by, specifically to maintain VLOS.
Whew! For a newbie like me, things can get complicated pretty quickly!
Just my two cents worth...
smp